Criss-cross heater for motor starter overload relay



May 17, 1966 v. MITCHNICK Em. 9,251,969

CRISS-CROSS HEATER FOR MOTOR STARTER OVERLOAD RELAY Filed June l5, 19632 Sheets-Sheet l May 17, 1966 v. MITCHNICK ETAL 3,251,969

CRISS-CROSS HEATER FOR MOTOR STARTER OVERLOAD RELAY Filed June 13, 19632 S1'1eecs--SheerI 1 United States Patent t O 3,251,969 CRISS-CROSSHEATER FOR MQTOR STARTER OVERLGAD RELAY Victor Mitchnick, Southfield,and Alva ll. Powell, Jr., Roseville, Mich., assignors to I-T-E CircuitBreaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed.lune 13, 1963, Ser. No. 287,726 3 Claims. (Cl. 20o-122) Our inventionrelates to an overload relay and, more particularly, is directed to anovel construction for the heater element whereby the parts arepositioned and constructed to gain maximum lbenefit from the inherentcharacteristics of the components.

The contactor to which our invention can be applied is described indetail in copending application U.S. Serial No. 189,915 tiled April 24,1962 in the names of John B. Cataldo et al., entitled Electrical Deviceand assigned to the assignee of the instant invention. An overloadrelay, in which our invention is particularly applicable, is illustratedand described in copending application U.S.

Serial No. 225,044 tiled September 20, 1962, in the names.

of Robert W. Thomas and Elwood T. Platz, entitled Overload Relay forMotor Starter, also assigned to the assignee of the instant invention.

In an overload relay for a contactor, the sensing element consists of abimetal which is actuated by a heater. In many overload relays there areranges of current which pass directly through the heater where thetemperatures of the terminals to the heater and overload relay becomeexcessive even though the heater does not radiate sufficient heat toactuate the bimetal. That is, the permissible temperature rise of theoverload relay terminals is exceeded even though there is insufficientheat generated by the heater to actuate the bimetal. This condition canexist because the temperature of the overload relay terminals isiniiuenced byv at least two factors, namely, the actual heat generatedby the heater itself, as well as the particular temperature distributionalong the whole thermal path including the heater.

Commercial contactors and overload relays have limitations with regardto the allowable temperature rise of the terminals which usually permitsthe temperature rise of the line terminals to be higher than theallowable temperature rise for the load terminals. In one typicalstandard, the load terminal is permitted a temperature rise of only 50C., whereas the line terminal is permitted a temperature rise of 65 C.Thus, if the line and load terminals are exposed to the same temperatureconditions, the severe temperature rise limitation for the load terminalwill result in an extreme limitation on the construction and materialsto be used in the overload relay. In the prior art, means have beenprovided to modify the temperature distribution in order to partiallyeliminate the aforementioned problem. In these prior art constructionsin which the heater is directly heated and of a U-shaped configuration,the heater is constructed with each leg of the U made of a differentmaterial, wherein the leg adjacent the bimetal is of high electrical andthermal resistance material and the leg furthest from the bimetal beingof low electrical and thermal resistance and being essentially a heatsink.

With this arrangement, a given current magnitude through the heater willheat the leg adjacent the bimetal to a higher temperature and thuspermit actuation of the bimetal at a current magnitude in which thetemperature rise in the leg of the heater removed from the bimetal islow. In other words, in some instances actuation of the bimetal ispermitted with terminal temperatures remaining within allowabletemperature rise standards. However, this desired result is obtainableonly when the construction of the overload relay issuch that the load3,251,969 Patented May 17, 1956 terminal can be connected to the lowresistance leg of the U-shaped heater since the permissible temperaturerise of the load terminal is substantially less than the permissibletemperature rise of the line terminal.

Unfortunately, some overload relays are constructed such that the loadterminal is adjacent the bimetal and, thus, with a U-shaped heater, theload terminal would be connected to the high resistance leg of theheater and, thus, the desired results would be either substantiallyreduced or eliminated. A typical prior art construction in which theload terminal is mounted adjacent the bimetal is shown and described inthe aforementioned copending application U.S. Serial No. 225,044. Thus,in this prior art arrangement there are ranges of current magnitudewhere it is possible that even though the U-shaped heater, including thehigh resistance leg adjacent the bimetal, would not generate suii'cientheat to actuate the bimetal and still exceed the allowable temperaturerise of the load terminal.

It is a primary object of our invention to provide a construction forthe heater of an overload relay in which, although the load terminal isadjacent the bimetal, the heater will always actuate the bimetal withoutcreating excessive temperature rises at the load terminal.

Essentially we provide a criss-cross arrangement in which the hightemperature material is connected to the line terminal which has alarger permissible temperature rise than the load terminal which, inturn, is connected to the low temperature rise leg of the heater.Furthermore, the high temperature portion of the heater is positionedparallel and adjacent to the bimetal so that the maximum benefit can beobtained for actuating the bimetal Without exceeding allowabletemperature rises.

Thus, the primary object of our invention is to provide an arrangementwhereby the bimetal can be actuated from a heater without exceeding thepermissible temperature rises of the load terminal.

Another object of our invention is to provide a heater for an overloadrelay in which, although the load terminal is positioned adjacent thebimetal, a novel criss-cross arrangement for the heater permits the highresistance material of the heater to be mounted adjacent the bimetal andstill be connected to the line terminal.

These and other objects of our invention will be-apparent from thefollowing description when taken in connection with the drawings, inwhich:

FIGURE 1 is an exploded perspective view of an overload relay and, inparticular, shows an exploded perspective view of our novel criss-crossheater.

FIGURE 2 is a side view of the overload relay of FIG- URE 1 with thecover removed and shows our novel heater.

FIGURE 2a is a composite side and cross-sectional View similar to FIGURE2 but illustrates the movement of the bimetal when it is actuated by ournovel heater.

FIGURES 3a, 3b and 3c are a side, top and end View, respectively, of ournovel criss-cross heater.

Referring now to the FIGURES l through 3, there is shown an overloadrelay containing our novel electric heater .10. It should be noted thatthe overload relay to which our heater can be applied and the oneillustrated in FIGURES l through 3 is shown and described in theaforementioned copending application, U.S. Serial No. 225,044. The basicelements of the device consists of the control contacts 32-33 and 43-44,the adjustment device including the means 28, the lost motion connectorsincluding the transfer ybar 31, and the external controls including theslide 50.

It is noted that the heater circuit of the overload relay is constructedso that the heater terminals are readily `accessible from the externalportion of the casing and the heater 100, therefore, isreadily removableand replaceferably to the load terminals.

The purpose, function and desired .results of our novel crisscrossheater is described in detail in the introduction of the instantapplication. The specific construction is illustrated in the drawingsand is as follows.

The heater 100 is comprised of a first member or .section 103 which is ahigh resistance member and located in a first plane substantiallyparallel to the bimetal 21. The first member 103 has an end portion 102which is conne-cted to the frstor line terminal 16 and the second memberor section 101 has an end member 104 connected to the load or secondterminal 17. A member 105, which is illustrated as an integral part ofthe second member 101 electrically connects the first member 103 to thesecond member 101. The connecting means 105 couldbe an integral part ofthe first member 103 or an independentr connection. The first member 103has a higher resistance as compared to the second member 101 which has alow resistance. Preferably the member 101 is made of copper so as toserve as a heat sink with respect to the high resistance first member103.

As seen in the figures, the line terminal 16 is connected to the highresistance member 103 by means of the Vscrew 20 passing through theopening 20a in extension 102 and the low resistance member 101 isconnected to the line terminal v17 by means of the screw 19 passingAthrough the opening 19a of the extension 104. Thus,

the first or line terminal 16, which has a high permissible temperaturerise, is connected by means of the extension 102 to the first member103, and the second or load terminal 17, on the other hand, has a lowpermissible temperature rise and it is properly connected thus to thesecond or low resistance member 101.

Since the first member 103 is in close proximity to the bimetal 21, theheat generated by current flowing through this high resistance memberwill immediately be absorbed by the bimetal 21, thereby causingdeflection of the bi- `metalaway from the heater as illustrated in thedotted the dotted position seen in FIGURE 2a to the solid position seenin FIGURE 2a thereby closing the cooperating contacts 43, 44 and openingthe cooperating contacts 32 and 33. v

The illustration shown in the gures is a preferred embodiment of myinvention and, as heretofore noted, arises from the problem that theload terminal 17 is located closer to the bimetal 21 than the lineterminal 16 but the temperature rise permitted for the load terminal 17is lower than the temperature rise permitted for'the line terminal.However, since the high resistance member 103 must be adjacent thebimetal 21, we have provided a novel criss-cross arrangement whereby thehigh resistance member 103 is located adjacent the bimetal 21 isconnected to the line terminal 16 located furthest from the bimetalwhereas the low resistance member 101 is connected to the load terminal17.

We have shown a single structural arrangement to achieve t-hese resultsbut it should be apparent to those skilled in the art that otherstructural arrangements could be used in order to achieve the desiredresults and still be within the con-cept as previously set forth.

Although we have described preferred embodiments of our novel invention,many variations and modifications will now be obvious to those skilledin the art, and we prefer, therefore, to be limited not by the specificdisclosure herein but only by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

What is claimed is:

1. An overload device including'a housing, a first and a second fixedterminal mounted to said housing and positioned externally thereof, abimetal, a heater, contact means, and additional means exclusive of saidheater extending between said bimetal and said contact means foroperation of the latter upon a predetermined defiection of the bi-metal;said bimetal, said heater, said contact means and said additional meansall mounted within said housing; said heater including a first and asecond portion connected to said first and said second terminals,

respectively, said portions connected in series with each other andcomprising a series circuit extending between said terminals; saidseries circuit being exclusive of said contact means; said first portionhave a higher electrical resistivity than said second portion; saidbimetal posisheet material with said first portion having a major.

portion thereof in a first plane generally at right angles to a secondplane wherein a major portion of said second portion is disposed; saidbimetal comprising a generally planar strip positioned in a third planegenerally at right `angles to said second plane; said heater beingconnectible to circuitry external of said device solely through saidfirst and second terminals.

3. An overload device as set forth in claim 1 in which said bimetal isspaced from said heater when said predetermined deliection takes place;said device also including means removably mounting said heater to saidfirst and second tenminals.

References Cited by the Examiner UNITED STATES PATENTS 2,824,941 2/.1958Fry 200-122 2,897,319 7/1959 WolfiF 200-122 2,994,754 8/1961 lWebking200--138 3,015,007 12/1961 Howard 200--114 3,023,288 2/1962Bodenschatzet al. 20G-122 3,031,551 4/1962 White et al. 200-122 BERNARDA. GILHEANY, Primary Examiner.

L. A. WRIGHT, Assistant Examiner.

1. AN OVERLOAD DEVICE INCLUDING A HOUSING, A FIRST AND A SECOND FIXEDTERMINAL MOUNTED TO SAID HOUSING AND POSITIONED EXTERNALLY THEREOF, ABIMETAL, A HEATER, CONTACT MEANS, AND ADDITIONAL MEANS EXCLUSIVE OF SAIDHEATER EXTENDING BETWEEN SAID BIMETAL AND SAID CONTACT MEANS FOROPERATING OF THE LATTER UPON A PREDETERMINED DEFLECTION OF THE BIMETAL;SAID BIMETAL, SAID HEATER, SAID CONTACT MEANS AND SAID ADDITIONAL MEANSALL MOUNTED WITHIN SAID HOUSING; SAID HEATER INCLUDING A FIRST AND ASECOND PORTION CONNECTED TO SAID FIRST AND SAID SECOND TERMINALS,RESPECTIVELY, SAID PORTIONS CONNECTED IN SERIES WITH EACH OTHER ANDCOMPRISING A SERIES CIRCUIT EXTENDING BETWEEN SAID TERMINALS; SAIDSERIES CIRCUIT BEING EXCLUSIVE OF SAID CONTACT MEANS; SAID FIRST PORTIONHAVE A HIGHER ELECTRICAL RESISTIVITY THATN SAID SECOND PORTION; SAIDBIMETAL POSITIONED IN CONFRONTING RELATIONSHIP WITH SAID FIRST PORTIONIN PROXIMITY SO THAT HEAT GENERATED BY CURRENT FLOW THROUGH SAID FIRSTPORTION HEATS SAID BIMETAL CAUSING DEFLECTION THEREOF; SAID BIMETALPOSITIONED CLOSER TO SAID SECOND TERMINAL THAN TO SAID FIRST TERMINAL.